Internal combustion engines of two-stroke or four-stroke type usually are equipped with a fuel supply system of carburetor type or injection type. In a carburetor, the throttle of the carburetor is affected by the operator's demand, so that wide open throttle produces a minimum throttling in the carburetor barrel. The depression created by the passing air in the carburetor venturi draws fuel into the engine.
Diaphragm-type carburetors are particularly useful for hand held engine applications wherein the engine may be operated in substantially any orientation, including upside down. Such carburetors typically include a fuel pump that draws fuel from a fuel tank and feeds the fuel to a fuel pressure regulator via a needle valve. The fuel pressure regulator usually includes a fuel metering chamber that stores fuel fed from the fuel pump and the fuel metering chamber is generally separated from atmosphere by a diaphragm that adjusts the fuel pressure to a constant pressure. The needle valve opens and closes the fuel passage from the fuel pump to the fuel metering chamber as the diaphragm moves. From the fuel metering chamber fuel is delivered to the main air passage via a main channel and an idle channel. The main channel leads to a main nozzle in the main air passage fluidly prior to the throttle valve, whereas the idle channel leads to an idle nozzle fluidly shortly after the throttle valve.
Local environmental conditions, such as temperature and altitude, as well as engine loading and fuel type used can affect engine performance. For instance, engines operated in cold weather require additional fuel, since cold conditions inhibit fuel vaporization and cold air is denser, requiring additional fuel to achieve the proper fuel/air ratio. At higher altitudes, the air is less dense, and less fuel is required to obtain the proper fuel/air ratio. Different fuel qualities may also affect the air-fuel ratio, for instance due to the amount of oxygen in the fuel. The engine may also behave differently at start-up, warm-up, acceleration and deceleration. All of these factors have an effect on the amount of fuel required for an optimal fuel-air ratio; it is therefore desirable to be able to easily affect the air-fuel ratio during operation of the engine.
Traditionally, carburetor engines have been equipped with stationary nozzles or manually adjustable nozzles to regulate the air-fuel ratio. However, as the demands on lower fuel consumption jointly with demands on cleaner exhaust have increased also electronically controlled nozzles have been suggested, for instance by having a solenoid valve in the passage between the fuel metering chamber and the nozzles in the main air passage, as e.g. in U.S. Pat. No. 5,732,682. While generally effective in reducing the harmful emissions to the atmosphere, the carburetors having solenoid valves are more costly and may require more time in assembly, thereby increasing the total costs associated with the manufacture of the carburetors. Another problem using fuel valve of solenoid type have been increased power consumption.
In particular when the engine is running at idle; the energy produced is low, and it is therefore advantageous that the engine can be controlled in such manner that the energy consumption is kept low during idle.
One parameter for controlling the air fuel ratio is the angular position of the throttle valve, which can be derived from a throttle position sensor. A known throttle position sensor includes a hall sensor and a magnet for detecting the full-open position of a butterfly throttle valve corresponding to the full throttle state of an internal combustion engine. A movable portion provided with a magnet rotates together with the throttle valve and has an end position corresponding to the full-open state of the throttle valve. A digital type of hall sensor is provided and being arranged to generate one of two possible signal values depending on whether it is actuated by said magnet or not actuated. The magnet on the movable portion is disposed so as to actuate the hall sensor when the movable portion is in said end position, whereby an output signal is generated by the hall sensor, which output signal is processed by signal processing means. What is referred to as a hall sensor often includes both the actual hall sensor and an integrated circuit (IC) amplifier.
The major drawback with a throttle position sensor of the type mentioned above is that it only provides a possibility to detect the full throttle state of the internal combustion engine and it is not possible to distinguish between part throttle and idle.
A conventional throttle position sensor which is often referred to as a rotation angle detector also has a magnet, rotating together with the throttle valve. Depending on the angle of the magnet, the magnetic field strength will vary at the position of a hall sensor and the output voltage of the hall sensor changes continuously in accordance with the strength of the magnetic field and the therefore also with the opening degree of the throttle valve. The output signal of the hall sensor can be processed by a signal processing means to be translated into an angle. The characteristics of a hall sensor vary e.g. with temperature and therefore, a temperature sensor can be provided for measuring the temperature of the hall sensor so as for a correcting means to apply the correct compensation at different temperatures of the hall sensor. What is referred to as a hall sensor often include both the hall sensor and an integrated circuit (IC) amplifier.
Often fuel supply units provided with such angle detectors are expensive and complex and have to be customized for the specific application, which means they are only offered by a very small number of suppliers.